RELATED PARTY TRANSACTIONS (Details) $ in Thousands		3 Months Ended		6 Months Ended
	Apr. 01, 2010 USD ($) Bcf	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)	Mar. 31, 2019 USD ($) Bcf / d contract	Mar. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)
Related Party Transaction [Line Items]
Demand fees expense recognized pertaining to related party agreement		$ 2,144	$ 2,087	$ 4,329	$ 4,236
Demand fees payable		1,154		$ 1,154		$ 1,150
Number of asset management agreements | contract				5
NJNG to NJRES Affilate
Related Party Transaction [Line Items]
Asset management agreement, period	10 years
NJNG to Steckman RIdge Affiliate
Related Party Transaction [Line Items]
Natural gas sold at cost under asset management agreement (in Bcf) | Bcf	3
Approximate annual demand fees under agreement	$ 9,300
Demand fees expense recognized pertaining to related party agreement		1,443	1,407	$ 2,916	2,855
Demand fees payable		778		778		775
NJRES to Steckman Ridge Affiliate
Related Party Transaction [Line Items]
Demand fees expense recognized pertaining to related party agreement		701	$ 680	1,413	$ 1,381
Demand fees payable		$ 376		$ 376		$ 375
NJNG to PennEast Affiliate
Related Party Transaction [Line Items]
Transportation precedent agreement, period				15 years
Transportation capacity under precedent agreement from NJNG with PennEast (in bcf per day) | Bcf / d				0.18